Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Depositing predominantly alloy coating
Reexamination Certificate
1999-03-19
2001-06-19
Mayekar, Kishor (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Depositing predominantly alloy coating
C205S240000, C205S241000, C205S242000, C205S244000, C205S246000, C205S254000, C205S255000, C205S274000, C205S281000, C205S296000, C205S302000, C205S311000, C106S001210, C106S001250
Reexamination Certificate
active
06248228
ABSTRACT:
BACKGROUND OF THE INVENTION
Electroplating solutions are usually aqueous. Every plating solution contains ingredients to perform at least the first, and usually several, of the following functions: (1) provide a source of ions of the metal(s) to be deposited; (2) form complexes with ions of the depositing metal; (3) provide conductivity; (4) stabilize the solution against hydrolysis or other forms of decomposition; (5) buffer the pH of the solution; (6) regulate the physical form of the deposit; (7) aid in anode corrosion; and (8) modify other properties peculiar to the solution involved.
The present invention improves the plating performance of the solution, particularly by increasing the useful current density over previously accepted norms The current density is the average current in amperes divided by the area through which that current passes, the area is usually nominal area, since the true area for any but extremely smooth electrodes is seldom known. Units used in this regard are amperes per square meter (A/m
2
).
It is generally in the best interest of efficiency to run electroplating baths at as high a current density as possible, while maintaining the desired quality of the plating finish. The higher the current density, the faster the metal coating plates on the surface. The current is carried by the ions in these baths and each type of ion has its own specific conductance. In a plating bath, however, ionic conductance is only one variable that must be considered in choosing an electrolyte. The final criterion is the quality of the coating at the desired current density.
Halide Baths
Plating baths with the main electrolyte being a halide ion (Br
−
, Cl
−
, F
−
, I
−
) have been used for many decades. See for example, U.S. Pat. Nos. 4,013,523, 4,053,374; 4,270,990; 4,560,446 and 4,612,091. The main halide ions in these baths have been chloride and fluoride. The metals plated from these baths typically include tin, nickel, copper, zinc, cadmium and alloys of these metals. As with all other types of baths it has been found that improvements on the performance of the bath can be made by incorporating additives into the bath. For example, U.S. Pat. Nos. 5,628,893 and 5,538,617 describe additives which can be used in a halogen tin plating bath for the purpose of reducing sludge formation by stabilizing the tin against oxidation.
There are many other properties of a bath that can be improved by additives. All of these properties are basically concerned with either the efficiency of the bath itself the quality of the deposit or the reduction of environmental effects. For example the additives for the tin bath described in U.S. Pat. Nos. 5,628,893 and 5,538,617 improve the efficiency of the bath and by decreasing the amount of waste also reduce the environmental effects.
SUMMARY OF THE INVENTION
The present invention relates to the use of alkali metal, alkaline earth metal, ammonium and substituted ammonium salts of alkyl and alkanol sulfonic acid which have been found to improve the performance of halide electroplating baths. When used in these electroplating baths these salt additives were found to generally increase the plating range so that these baths can be used at much higher current densities than previously. Thus these baths can be run at greater speeds than those without these additives. Further improvements are seen in the quality of the deposits.
Thus, the present invention is directed to a method of improving the plating performance of an aqueous halide ion based electroplating bath comprising the step of adding an effective performance enhancing amount of a salt of an alkyl and/or alkanol sulfonic acid to said bath. In preferred embodiments, the halide ion of the bath is usually either chloride or fluoride.
The salts used to improve the bath plating performance characteristics are particularly selected from the group consisting of alkali metal, alkaline earth metal, ammonium and substituted ammonium salts. Especially preferred are salts of 2-hydroxy ethyl sulfonic acid, especially the sodium salt (sodium isethionate).
The baths that can be improved by the present invention include tin and tin alloy plating baths; nickel and nickel alloy plating baths; copper and copper alloy plating baths; zinc or zinc alloy plating baths; as well as cadmium and cadmium alloy plating baths.
DETAILED DESCRIPTION OF THE INVENTION
The use of alkali metal, alkaline earth metal, ammonium and substituted ammonium salts of alkyl and alkanol sulfonic acids as additives in pure metal and metal alloy halide electroplating baths has a number of unexpected benefits including wider useful current density range and improved appearance. The metals and metal alloys include, but are not limited to tin, lead, copper, nickel, zinc, cadmium, tin/zinc, zinc
ickel and tin
ickel.
These salts are not harmful to the environment, they are completely biodegradable and the products of the biodegradation are common ions and molecules found in the environment. In addition they have a number of other advantages including high solubility, low corrosivity to equipment, good stability at high temperatures, and compatibility with many other metal salts.
These baths also contain the corresponding metal salt or metal salts if an alloy plate is required, and various additives to control the quality and appearance of the plated surface and the stability of the bath solution. Typical additives include a surfactant such as an ethoxylated fatty alcohol, a brightening agent if required and an antioxidant such as hydroquinone or catechol, if tin is one of the metals being plated.
The tin in these baths is in the stannous or reduced form. If oxidation occurs the tin will be converted to the stannic or oxidized form which then commonly precipitates to form a sludge. This process adds to the inefficiency of these baths and also creates a requirement for constant filtering. Prior art patents, for example U.S. Pat. Nos. 4,717,460, 5,538,617 and 5,562,814 describe products that can decrease the amount of tin being oxidized.
The present invention will be further illustrated with reference to the following example which will aid in the understanding of the present invention, but which is not to be construed as a limitation thereof All percentages reported herein, unless otherwise specified, are percent by weight. All temperatures are expressed in decrees Celsius.
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Fernandes Brenda
Gillman Hyman D.
Wikiel Kazimierz
Banner & Witcoff , Ltd.
Linek Ernst V.
Mayekar Kishor
Technic, Inc. and Specialty Chemical System, Inc.
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